Page 242 - Carbon Nanotube Fibres and Yarns
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232   Carbon Nanotube Fibers and Yarns


          ρ(T) measurements on a composite fiber stretched by 53% and an annealed
          one stretched by 76% displayed in Fig. 9.9B shows that ρ for the composite
          fiber exceeds that of the annealed one by four to five orders of magnitude
          at 300 K. This suggests that not just the morphology of the two fibers but
          the conduction mechanisms in the two morphologies affects their ther-
          moresistive properties. Le et al. [8] determined the thermoresistive response
          of the free CNT yarns and the CNT yarns integrated in a polymer matrix
          subjected to heating and free cooling cycles (Fig. 9.10). The thermoresis-
          tive behavior of a selected sample under three heating/cooling cycles as



                              Thermocouple
                 Fluke 298                      Sample          Oven’s
                                                             heating plate









              T(°C)
                                       Agilent 34411A
                              R(Ω)



            (A)  Data acquisition



              1                               1
                             Sample #1 - cycle 1
              0              Linear fit       0
             −1                              −1             (∆R/R 0 ) res
             −2                              −2
            ∆R/R 0 (%)  −3  −2              ∆R/R 0(%)  −3  Hα          (∆R/R 0 ) max
                                             −4
             −4
             −5  α∼−2.34×10                  −5
             −6                              −6
             −7                              −7    Sample #1 - cycle 1
             −8                              −8
                0  50  100  150  200  250  300  350  0  50  100  150  200  250  300  350
           (B)           ∆T/T 0 (%)        (C)            ∆T/T 0 (%)
          Fig.  9.10  (A) Schematic representation of  the  thermoresistive  measurement  system
          [8].  (B)  Linear  fit  of CNT  fiber  monocomposite sample  during  first heating  section.
          (C)  A  hysteretic  cycle  showing  the  parameters  obtained  from  the  thermoresistive
          characterization [8]. (Source: H.H. Le, G. Brodeur, M. Cen-Puc, J.J. Ku-Herrera, F. Avilés, J.L.
          Abot, Piezoresistive and thermo-piezoresistive response of constrained carbon nanotube
          yarns towards their use as integrated sensors, in: Proceedings of 31st American Society for
          Composites Conference, Williamsburg, VA, 2016.)
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